Progressive formation of neuritic plaques and neurofibrillary tangles is exponentially related to age and neuronal size. A morphometric study of three geographically distinct series of aging people.

Neuronal size and the incidence of neuritic plaques (NPs) and neurofibrillary tangles (NFTs) were morphometrically and quantitatively studied in the entorhinal cortex of 300 autopsied individuals without dementia in three geographically distinct series (Brazil, Germany and Japan), and an additional series including 30 clinically diagnosed Alzheimer's disease patients. The mean ages at onset of NPs and NFTs were similar between the three normal series, and the incidence of NPs and NFTs increased exponentially with age, but at different rates. A correlation was found between larger neuronal size and higher incidence of NPs and NFTs. Neuronal size distribution largely seemed to account for the differences between the series. While the onset of neurodegeneration may be tightly programmed, i.e., in a species-specific manner, our data support the idea that the incidence of NPs and NFTs and the progression from NPs to NFTs may vary remarkably, depending on neuronal size.